Several medical treatments have been developed which use invasive medical devices for local in situ delivery of energy within body tissues, such as for example in order to treat cancer, or according to other specific examples for preventing or reducing restenosis. Restenosis is an occlusive tissue response to vessel wall injury after recanalization of an occluded region of the vessel, such as through angioplasty, stenting or atherectomy, and has been observed to take place during the first six months after recanalization. Restenosis is believed to be related to an injury response in a vessel wall after balloon expansion of an occlusive lesion, in the case of angioplasty and/or stenting, or during debulking of the lesion site, in the case of atherectomy procedures. This wall injury is further believed to invoke a hyperproliferative response in the smooth muscle cells which make up the vessel wall, such that the proliferating muscle tissue essentially grows into the vessel lumen. This muscle cell proliferation forms at least in part an occlusion at the injury site, minimizing or even reversing the initial result of recanalization. Various localized energy delivery devices which have been disclosed for use in preventing restenosis are generally intended to stunt this hyperproliferative growth of smooth muscle cells in order to substantially reduce the related occlusive response and thereby maintain lumenal patency through the injured site post-recanalization.
According to the known devices which are intended for localized energy delivery to tissue, various specific modes of local energy delivery have been previously disclosed. For example, one known procedure for treating tumors uses a catheter to deliver a ferromagnetic material to a tumor so that the material may heat the tumor when exposed to an ultrahigh radiofrequency electromagnetic field or ultrasonic waves. In another example intended to treat atherosclerosis, microscopic magnetic particles are injected intravenously into a patient, are selectively phagocytized by atherosclerotic cells in a lesion along a blood vessel wall in the patient, and are then heated to therapeutic temperatures by subjecting the magnetized cells to a high frequency alternating magnetic field. Another previously disclosed medical device assembly is adapted to locally emit X-ray radiation into tissue adjacent the catheter. Still further, another known device intended for use in preventing restenosis is adapted to emit ultraviolet light radiation into injured vessel wall tissue. More detailed examples of medical device assemblies and methods which are adapted for local delivery of high levels of energy into tissue, such as of the types just described, are variously disclosed in the following references: U.S. Pat. No. 4,359,453 issued to Gordon; U.S. Pat. No. 5,282,781 issued to Granov et al.; U.S. Pat. No. 5,607,419 issued to Amplatz et al.; and PCT No. WO 97/07740.
Other known devices and related procedures place a radioactive source made of a radioisotope material within a particular body region in order to locally irradiate specific tissue abnormalities within that body region. Such procedures are herein generally referred to interchangeably as "radiation therapy" or "brachytherapy" or "radiotherapy", and include applications which actually treat as well as prevent abnormal conditions in tissue. Medical device assemblies which are adapted for brachytherapy applications are herein interchangeably referred to as tissue "radiation devices" or "brachytherapy devices", or "radiation therapy devices"
Previously disclosed brachytherapy devices include permanent implantable brachytherapy devices, which are adapted for prolonged brachytherapy of tissues, and temporary implantable brachytherapy devices, which are adapted for brachytherapy of tissue. In addition, particular brachytherapy devices have also been disclosed for specialized use in treating specific tissues, including cancer tumors or injured vessel wall tissue for preventive restenosis therapy.